The present invention relates to a radial milling head, in particular for thread milling.
As to the prior art, it is referred to German patent 23 35 651 and in particular to German patent 24 41 387 disclosing an advanced embodiment of a radial milling head disclosed in the German patent first referred to. A radial milling head comprises three rollers which are rotatably supported in a casing. Each roller is secured to a gear wheel, all three gear wheels meshing with a central gear wheel wich is rotatably supported in the casing. The equidistantly and peripherally spaced arrangement of the three rollers with respect to a central axis of the casing provides a gap for axially entering a workpiece which outer periphery is to be worked, for example to receive a threaded portion.
There is a locking and releasing mechanism which allows the rollers to perform a full rotation during each working cycle. The locking and releasing is controlled by a spring biased locking member which is secured to the central gear wheel. In the rest position of the rollers, in which flats provided on the peripheral surface of each roller are facing the central axis to make it possible that a tool enters between the rollers, the locking member is in a locking position in which the central gear wheel is fixed and cannot rotate. Upon releasing the locking member, the spring acting on the locking member rotates it together with the central gear wheel, thus rotating the rollers until they come into frictional engagement with the rotating workpiece. As soon as the frictional engagement is completed, the rollers are rotatably driven by the workpiece. The peripheral working surface of the rollers has an increasing diameter so that during this movement of rotation the workpiece is worked by the peripheral surface of the rollers to mill a thread, for example. Upon completion of a full-turn of the locking member and the central gear wheel, the locking member is again stopped by a locking pin. The working cycle has been completed.